The individual research projects which compose this Program Project each have needs of mice for use in histological and metabolic studies, to serve as sources of cells and tissues or for use in nutritional studies. Each mouse used for the studies proposed in the Program Project will be provided by the Animal Core. To meet this needs, the Core will maintain and breed mice for use in experiments, perform intercrosses between transgenic and knockout animals to generate new strains needed for proposed studies, genotype progeny of these crosses, routinely genotype progeny from maintenance breeding stocks in order to serve as a quality control check on regular breeding procedures and carry out all nutritional manipulations needed by the individual research projects which composed the Program Project. The Specific Aims of the Core are: Aim 1. To insure that sufficient animals are available to meet the research needs for each project of the Program Project; Aim 2. To breed and maintain animals during nutritional studies carried out by individual research projects and to provide quality control data on mice used for the nutritional studies; and Aim 3. To facilitate the sharing of animals, data and ideas between the individual research projects.